Does higher fuel octane rating mean better engine performance?

Gasoline prices are skyrocketing, and people are looking for the most bang for their buck. When filling up at the station, there are usually three kinds of gasoline on offer, standard, premium, and super-premium. Different car brands will offer you different names to accompany these products, but what determines their pricing is the research octane number (RON), and the higher the number, the more expensive fuel is. Fuel companies often advertise that higher octane allows more performance to be extracted out of the engine. To an extent, they’re right, but not totally. 

Octane is a hydrocarbon that can be found in gasoline. The chemical helps keep the engine’s combustion cycle predictable. Gasoline engines have spark plugs that ignite the air-fuel mixture to push the piston down with explosive force. Timing is key and making sure your fuel does not ignite while the piston is on the way up is important for engine reliability and power. 

A higher octane rating is required because an engine produces heat that could cause pre-ignition. Another factor is the compression ratio, which is a measure of how much the air is squeezed when the piston is at its highest point. The byproduct of this compression heat, and can also detonate fuel before it’s expected to; in fact, diesel engines ignite their fuel through this principle. Octane makes gasoline less volatile, by making it more heat-resistant. Only a spark plug should be able to ignite the fuel, not ambient temperatures. 

So why are there fuels with 91-93 RON? That’s because most gasoline-powered cars don’t need anything higher. Car manufacturers know what’s best for the machine they designed, hence they give a recommendation to the minimum RON that you need. If your engine is rated for 91 RON, there is no monumental incentive for going premium because your engine simply doesn’t need it. You may experience a marginal gain, but it’s small – borderline negligible. 

Unless your car is turbocharged, or a high-performance car, a higher-than-required octane rating won’t give you a substantial increase in power. The fuel doesn’t explode with more force, it withstands premature detonation more than a regular fuel does. Since there is no tangible benefit, that means that you’ll be wasting your money on high-octane fuel that your car does not need. So sorry to say, but your Mitsubishi Mirage will not benefit from premium fuels as a Toyota Supra can with its turbocharged inline-six. 

So, when do you need to run a higher octane fuel? Run it if the manufacturer tells you to. If the minimum RON is at 95, don’t fill your vehicle with 91 octane fuel. Another exception can be made for cars that are heavily modified or tuned. A higher octane fuel is safer than a lower one because when going above the manufacturer’s rated power rating, then the engine produces more heat. For turbocharged cars, more air is forced into the combustion chamber, and so a higher RON is required. In short, if your car is performing outside of the manufacturer’s specifications with a modification to the ECU, then a more premium fuel is advisable. Or you can ask your tuner to tailor your car to run at a lower octane, at the cost of potential power gains.